Metals, Non-Metals and Alloys

Why this topic matters for NDA

The NDA General Science paper (Chemistry portion) leans heavily on everyday chemistry, and metals and non-metals sit right at the centre of it. Almost every year you see at least two or three questions from this chapter.

The good news: these are recall questions, not long calculations. If you know that mercury is the only liquid metal, or that brass is copper plus zinc, you score in seconds. Defence applications – steel, aluminium alloys, the chemistry of corrosion – make this directly relevant to the armed forces too.

Across the NCERT Science books of Classes 6 to 10, this chapter is built up slowly – first you learn what metals and non-metals look like, then how they react, and finally how we extract and combine them. NDA simply tests the end-product of all that learning. So instead of cramming a few days before the exam, treat this page as a single-sitting revision that locks in every fact the paper can throw at you.

What are metals and non-metals?

All known elements are broadly classified as metals, non-metals or metalloids. About 80% of all elements are metals, and they sit mainly on the left and centre of the periodic table; non-metals cluster on the upper right.

The quick definitions

• Metals are elements that are usually hard, shiny, good conductors of heat and electricity, and tend to lose electrons to form positive ions (cations).
• Non-metals are usually dull, brittle (if solid) or gaseous, poor conductors, and tend to gain electrons to form negative ions (anions).
• Metalloids (e.g. boron, silicon, germanium, arsenic) show properties in between – silicon is the classic semiconductor.

How metallic character changes in the table

As you move left to right across a period, metallic character decreases – elements move from metals through metalloids to non-metals. As you move down a group, metallic character increases. This is why the most reactive metals (like caesium) sit at the bottom-left and the most reactive non-metals (like fluorine) sit at the top-right. Understanding this single trend lets you predict whether an unfamiliar element behaves like a metal or a non-metal.

Physical properties: how to tell them apart

Physical properties are the fastest way NDA tests this topic. Learn the contrast as a table in your head.

Properties of metals

• Lustre: shiny surface (metallic lustre).
• Malleable: can be hammered into thin sheets (gold and silver are the most malleable).
• Ductile: can be drawn into wires (gold is the most ductile).
• Conduction: good conductors of heat and electricity (silver is the best, then copper).
• Sonorous: produce a ringing sound when struck.
• Generally high melting and boiling points and high density.

Properties of non-metals

• Usually dull (no lustre – iodine and graphite are exceptions).
• Brittle when solid – they break or shatter, not bend.
• Poor conductors (graphite is the exception – it conducts electricity).
• Mostly low melting points; many are gases at room temperature.

Chemical behaviour of metals and non-metals

Chemically, the big difference is what each does with electrons during reactions.

Reaction with oxygen

• Metals form basic oxides. Example: sodium burns to give Na₂O, which dissolves in water to form a base (NaOH).
• Non-metals form acidic oxides. Example: sulphur burns to SO₂, which forms an acid in water.
• Some metal oxides (Al₂O₃, ZnO) are amphoteric – they react with both acids and bases.

Reaction with water and acids

• Reactive metals react with water to release hydrogen gas. Sodium and potassium react violently even with cold water.
• Metals above hydrogen in the reactivity series displace hydrogen from dilute acids, releasing H₂.
• Non-metals generally do not react with dilute acids to give hydrogen.

Why metals and non-metals behave so differently

Everything comes down to electrons in the outermost shell. Metals have 1, 2 or 3 valence electrons which they lose easily, becoming positive ions – this is why they are good reducing agents. Non-metals have 5, 6 or 7 valence electrons and prefer to gain electrons to complete their octet, becoming negative ions, which makes them good oxidising agents. When a metal and a non-metal react, electrons transfer from the metal to the non-metal, forming an ionic (electrovalent) compound such as sodium chloride (NaCl). When two non-metals combine, they share electrons, forming covalent compounds like carbon dioxide.

The reactivity series – your master tool

The reactivity (or activity) series arranges metals in decreasing order of how readily they react. It is the single most useful list in this chapter because it predicts displacement, extraction difficulty and corrosion.

What the series tells you

• A more reactive metal displaces a less reactive metal from its salt solution. Iron displaces copper: Fe + CuSO₄ → FeSO₄ + Cu.
• Metals above hydrogen (H) release hydrogen from acids; those below do not.
• Highly reactive metals (K, Na, Ca, Mg, Al) are found combined in nature and are hard to extract; unreactive metals (Au, Ag, Pt) occur in free/native state.

Extraction of metals (metallurgy basics)

Most metals occur as ores (minerals from which metal can be profitably extracted). The method of extraction depends on the metal's position in the reactivity series.

Key terms

• Mineral: naturally occurring compound of a metal.
• Ore: a mineral with enough metal to extract economically.
• Gangue: the unwanted earthy impurities in an ore.

Three broad routes

• Highly reactive metals (K, Na, Ca, Mg, Al) → extracted by electrolysis of molten salts (e.g. aluminium from alumina by the Hall–Héroult process).
• Moderately reactive metals (Zn, Fe, Pb, Cu) → the ore is roasted/calcined to oxide, then reduced with carbon (coke).
• Least reactive metals (Au, Ag, Pt) → found native; little or no chemical reduction needed.

Corrosion and rusting

Corrosion is the slow eating away of a metal surface by reaction with air, moisture or chemicals. Rusting is the specific corrosion of iron.

Examples of corrosion

• Iron rusts to a reddish-brown flaky coating.
• Copper develops a green coating (basic copper carbonate).
• Silver develops a black tarnish (silver sulphide) from sulphur in air.

How rusting is prevented

• Painting, greasing or oiling to block air and moisture.
• Galvanisation – coating iron with a layer of zinc.
• Electroplating and applying anti-rust solutions.
• Making alloys such as stainless steel.

What are alloys and why we make them

An alloy is a homogeneous mixture of a metal with one or more other metals or non-metals. Alloying changes properties to make the material more useful.

Why we alloy metals

• To increase strength and hardness (pure iron is soft; steel is strong).
• To improve resistance to corrosion (stainless steel does not rust).
• To lower melting point, change colour, or reduce electrical conductivity where needed.

How an alloy is made

Alloys are usually prepared by melting the parent metal and dissolving the other elements into it in a fixed ratio, then allowing the mixture to cool and solidify. Because the atoms of the added element are a different size, they disturb the regular arrangement of the metal's atoms. This makes the layers harder to slide over one another – which is exactly why alloys are harder and stronger than the pure metal they are based on. The same effect also lowers electrical conductivity, so pure copper, not brass, is used for electrical wiring.

Common alloys and their composition

This is pure marks-on-a-plate for NDA. Learn the composition of each common alloy.

Where they are used

• Brass – utensils, musical instruments, fittings.
• Bronze – statues, medals, bearings.
• Duralumin – aircraft bodies and frames (light yet strong).
• Solder – joining electronic and electrical connections.

Worked example: predicting a displacement reaction

Let's apply the reactivity series to a classic exam scenario.

This is why you must never store copper sulphate solution in an iron container – the iron would react with it.

Previous-year style question

Quick revision